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The successful demonstration of the “Aerostatic Seal” in a half scale rotating facility is described in this paper. The Aerostatic seal is a novel dynamic clearance seal specifically designed for steam turbine secondary gas path applications. The seal responds to radial rotor excursions, so a reduced clearance can be maintained compared to conventional labyrinth seal without damage to the seal. This enables increased turbine performance through reduced leakage and increased tolerance of turbine transient events typically found during start up. The seal is an extension of the existing retractable seal design already deployed in commercial steam turbines. The seal was tested in the Durham Rotating Seals Rig, which was developed specifically to test this device. The rig featured a rotor designed to run with large eccentricities to model high speed radial rotor excursions, and the seal was instrumented to measure the real time seal response to the rotor. The experimental campaign has conclusively demonstrated the ability of the seal to dynamically respond to the rotor position. The key result is that the seal is able to track the rotor position at high speed, and hence maintain a mean seal clearance that is lower than the rotor eccentricity. Overall this work marks a key milestone in the development of the Aerostatic Seal, and leads the way to testing in a steam environment and application in steam turbine plant.

This paper presents a series of experiments on the Aerostatic Seal, a dynamic clearance seal for steam turbine application first described at the 2015 ASME Turbo Expo (Paper Number GT2015-43471). This dynamic clearance seal moves with rotor excursions and so has the potential to deliver a smaller clearance than traditional seals. The concept is an extension of the retractable seal design which is widely used in existing steam turbines. The experimental program was carried out in a low cost static test facility using an aerostatic seal design. The seal exhibited a dynamic clearance response and will therefore respond to rotor excursions. 3D CFD was also used to aid the understanding of flow features not captured by the analytical design tool. Adjustments to both the design process and to future seal designs are proposed in the body of the paper. This paper therefore describes an experimental proof of concept for the aerostatic seal and paves the way for future development in rotating facilities.

Effective sealing in turbomachinery reduces the leakage flow bypassing the turbine blades and also reduces the losses where the leakage flow mixes with the primary flow. In general the clearance should be as small as possible but is limited by thermal and mechanical effects which vary with load. In recent years intermittent energy sources, particularly wind and solar, have appeared in greater numbers on the power network. As a consequence conventional power plants need to become more flexible to accommodate renewable energy generation. A sealing technology which can accommodate rapid changes in load and maintain seal performance would be a valuable development.This paper presents a novel seal design for steam turbines. The seal is designed to be capable of maintaining a smaller clearance than that of conventional labyrinth seals whilst allowing for dynamic movement with the rotor. The paper describes the seal concept and the analytic al work undertaken to demonstrate the concept. The seal design has also been tested in test facilities at Durham and the initial experimental results are included. They show that the concept works as intended.Copyright © 2015 by ASME and Alstom Technologie AG